Advances in paediatric clinical pharmacology are interdependent with a better understanding of the influence of growth on drug disposition and action. In this field, there is an increasing need for non-invasive drug monitoring approaches. This paper aims to discuss the role of positron emission tomography in such practice. This molecular imaging technique enables the determination of the distribution of a drug radiolabelled with a positron-emitting radionuclide. Able to directly assess both pharmacokinetic and pharmacodynamic events in humans, positron emission tomography provides a new perspective on paediatric drug research. Although placing this technique in a unique position to potentially contribute to the process of drug development and evaluation in paediatrics, several ethical and methodological aspects should be considered.